The risk of cancer from such radiation is already known about, but now scientists think there would also be an increased risk of late degenerative disorders, including Alzheimers - and that's not so understood.

The new paper showed that, at least in mice, similar types of radiation as that found in deep space led to increases of "Aβ plaque pathology " - changes in the brain which could lead to Alzheimer's.

The research by the University of Rochester Medical Center Department of Neurobiology and Anatomy used particle accelerators at Nasa's Space Radiation Laboratory to expose the animals to the highly radioactive particles.

"These findings clearly suggest that exposure to radiation in space has the potential to accelerate the development of Alzheimer's disease," said the study's author Dr. M. Kerry O'Banion.

It's not quite a reason to abandon space travel, but it could be evidence that we'll need more than a big rocket (and a big Christmas tree) to get somebody to another planet alive any time soon.